The University of California, Santa Barbara (UC Santa Barbara or UCSB) is a public land-grant research university in Santa Barbara County, California, United States. Tracing its roots back to 1891 as an independent teachers college, UC Santa Barbara joined the University of California system in 1944. It is the third-oldest campus in the system, after UC Berkeley and UCLA.

UCSB's campus sits on the oceanfront site of a converted WWII-era Marine Corps air station. UCSB is organized into three undergraduate colleges (Letters and Science, Engineering, Creative Studies) and two graduate schools (Education and Environmental Science & Management), offering more than 200 degrees and programs. It is classified among "R1: Doctoral Universities – Very high research activity" and is regarded as a Public Ivy. The university has 12 national research centers and institutes, including the Kavli Institute for Theoretical Physics and NSF Quantum Foundry. According to the National Science Foundation, UC Santa Barbara spent $305.48 million on research and development in fiscal year 2023, ranking it 105th in the nation. UCSB was the No. 3 host on the ARPAnet and was elected to the Association of American Universities in 1995.

UCSB alumni, faculty, and researchers have included 7 Nobel Prize laureates, founders of 90+ companies, 1 Fields Medalist, 50 members of the National Academy of Sciences, 34 members of the National Academy of Engineering, and 56 members of the American Academy of Arts and Sciences. The faculty also includes two Academy and Emmy Award winners and recipients of a Millennium Technology Prize, an IEEE Medal of Honor, a National Medal of Technology and Innovation and a Breakthrough Prize in Fundamental Physics.